Method and system for oxidatively increasing cetane number of hydrocarbon fuel

ABSTRACT

High energy (e.g., ultrasonic) mixing of a hydrocarbon feedstock and reactants comprised of an oxidation source, acid, and optional catalyst yields a liquid hydrocarbon product having increased cetane number. Ultrasonic mixing creates cavitation, which involves formation and violent collapse of micron-sized bubbles, which greatly increases reactivity of the reactants. Cavitation substantially increases cetane number compared to reactions carried out using conventional mixing processes, such as simple mechanical stifling. An aqueous mixture comprising water and acid can be pretreated with ozone or other oxidizer using ultrasonic cavitation prior to reacting the pretreated mixture with a hydrocarbon feedstock to promote cetane-increasing reactions. Controlling temperature inside the reactor promotes beneficial cetane-increasing reactions while minimizing formation of water-soluble sulfones.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/877,484, filed Sep. 8, 2010, which claims the benefit ofearlier filed U.S. Provisional Application No. 61/243,053, filed Sep.16, 2009, the disclosure of which is incorporated herein in itsentirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention is in the field of hydrocarbon fuels, moreparticularly in the field of processing hydrocarbons, such as diesel andbiodiesel, in order to increase the cetane number.

2. The Relevant Technology

Cetane number is a measurement of the combustion quality of diesel fuelduring compression ignition. It is a significant expression of dieselfuel quality among a number of other measurements that determine overalldiesel fuel quality. Cetane number is actually a measure of a fuel'signition delay, which is the time period between the start of injectionand start of combustion (ignition) of the fuel. For any given dieselengine, a higher cetane fuel will have a shorter ignition delay periodthan a lower cetane fuel.

Generally, diesel engines run well with a cetane number from 40 to 55.Fuels with higher cetane numbers and shorter ignition delays providemore time for the fuel combustion process to be completed. This, inturn, increases the extent and efficiency of combustion. Higher speeddiesel engines operate more effectively when using higher cetane numberfuels. Nevertheless, there is typically no performance or emissionadvantage when the cetane number is increased beyond approximately 55.Beyond this point, the fuel's performance hits a plateau.

By way of background, cetane is an un-branched, open chain, alkanemolecule that ignites very easily under compression, so it was assigneda cetane number of 100. Conversely, alpha-methyl napthalene was assigneda cetane number of 0. All other hydrocarbons in diesel fuel are indexedto cetane as to how well they ignite under compression. The cetanenumber therefore measures how quickly the fuel starts to burn(auto-ignites) under diesel engine conditions (i.e., compression andtemperature). Since there are hundreds of components in diesel fuel,with each having a different cetane quality, the overall cetane numberof the diesel is the average cetane quality of all the components. Thereis typically very little actual cetane in diesel fuel.

In North America, most states adopt ASTM D975 as their diesel fuelstandard, and the minimum cetane number is set at 40, with typicalvalues in the 42-45 range. Premium diesel fuels may or may not havehigher cetane numbers, which is supplier dependent. Premium diesel fuelsoften include additives to improve cetane number and lubricity,detergents to clean the fuel injectors and minimize carbon deposits,water dispersants, and other additives depending on geographical andseasonal needs.

In Europe, diesel cetane numbers were set at a minimum of 38 in 1994 and40 in 2000. The current standard for diesel sold in Europe is determinedby EN 590, with a minimum cetane index of 46 and a minimum cetane numberof 51. Premium diesel fuel can have a cetane number as high as 60 inEurope.

Additives such as alkyl nitrates (e.g., 2-ethyl hexyl nitrate),di-tert-butyl peroxide, and dimethyl ether are commonly used asadditives to raise the cetane number. Additives such as 2-ethyl hexylnitrate are very expensive, costing approximately $2200/ton, and cannotbe used in quantities greater than about 0.2% of the diesel fuel withoutbecoming cost prohibitive.

Biodiesel from vegetable oil sources have been recorded as having acetane number range of 46 to 52. Animal-fat based biodiesels cetanenumbers range from 56 to 60.

The cetane number of diesel fuel can also be increased by processingdiesel fuel having a lower cetane number to yield a diesel fuel having ahigher cetane number. For example, U.S. Pat. No. 5,114,434 to Praulus etal. describes a process by which viscoreduced diesel fuel is contactedwith hydrogen peroxide in a reactor that includes a stirring mechanism.While the process disclosed by Praulus et al. effectively increased thecetane number, the amount of increase was modest (i.e., the cetanenumber was increased from 39 to 50 in one example and from 39 to 53.5 inanother). Moreover, the residence time in the reactor was quite long,being 5 hours or more.

Other processes are designed to primarily desulfurize high sulfur fossilfuels by maximizing oxidation of sulfur-bearing molecules and formationof water-soluble sulfones that can be removed by phase separation. Anexample of such processes is described in U.S. Pat. No. 6,500,219 toGunnerman. In the case of high sulfur diesel, Gunnerman provide reactionconditions (e.g., preheating of the diesel, coupled with no cooling ofthe reaction) that promote oxidation of sulfur-bearing molecules, whileminimizing oxidation of other hydrocarbon molecules.

BRIEF SUMMARY OF THE INVENTION

It has now been unexpectedly found that much higher increases in cetanenumber of hydrocarbons is possible when utilizing an oxidative processin combination with cavitation compared to reactors that employconventional stirring. According to one embodiment, the reaction isessentially a two-phase reaction including an oil phase and aqueousphase. In another embodiment, it may be advantageous to introduce athird phase comprised of ozone gas.

Ultrasonic mixing results in “cavitation” in which tiny micron sizewater bubbles are formed and collapse, which causes an intense releaseof energy. The result is a product having increased cetane number, whichis typically higher than 55, preferably higher than 60. Sometimes theproduct can be characterized as “super cetane diesel,” as it can have acetane number that is higher than the applicable cetane number standard.This permits it to be used as a blending stock for stock diesel fuelshaving cetane numbers below a specified minimum value (e.g., between 40to 75) to yield a blended diesel fuel product having a cetane number ator above the specified minimum cetane standard. Super cetane diesels canhave a cetane number substantially higher than 60.

According to one embodiment, a method for increasing cetane number of ahydrocarbon includes:

-   -   providing a hydrocarbon feedstock having an initial cetane        number;    -   introducing the hydrocarbon feedstock into a reactor together        with an oxidation source, catalyst (plus fine filterable solids        to enhance cavitation), and acid; and    -   intimately mixing the hydrocarbon feedstock, oxidation source,        catalyst, and acid by means of cavitation in order to oxygenate        the hydrocarbon feedstock and thereby yield a modified liquid        hydrocarbon having a final cetane number that it at least about        15% higher than the initial cetane number.

According to another embodiment, a method for increasing cetane numberof a hydrocarbon includes:

-   -   introducing an oxidizer and an aqueous mixture comprised of        water and acid into an ultrasonic cavitation reactor;    -   subjecting the aqueous mixture and oxidation source to        ultrasonic cavitation to yield a pretreated aqueous mixture        having oxidating radicals;    -   introducing the pretreated aqueous mixture and a hydrocarbon        feedstock having an initial cetane number into an upgrading        reactor; and    -   mixing the hydrocarbon feedstock and the pretreated aqueous        mixture in the upgrading reactor to oxygenate the hydrocarbon        feedstock and yield a modified liquid hydrocarbon having a final        cetane number that it at least about 15% higher than the initial        cetane number.

According to one embodiment, the liquid hydrocarbon feedstock has aboiling point in a range of about 150° C. to about 380° C. Exemplaryliquid hydrocarbon feedstocks include one or more of refinery streams,straight petroleum runs, thermally cracked hydrocarbons, catalyticallycracked hydrocarbons, hydrocracked hydrocarbons, biodiesels, vegetableoils, palm oil, and animal fats. Alternatively or in addition, theliquid hydrocarbon feedstock can be a material produced by visbreaking amaterial such as bright stock, used lubricating oil, or gas oil with aboiling point in a range of about 200° C. to about 500° C. Suchmaterials typically have a boiling range above that of naphtha (i.e.,gasoline).

The disclosed methods utilize an oxidation source to oxygenate thehydrocarbon feedstock. The oxidation source may be one or more ofaqueous hydrogen peroxide, organic peroxide, inorganic peroxide, orozone. The oxidation source generates hydroxyl radicals and/or oxygenradicals in order to oxygenate the liquid hydrocarbon feedstock. Becausemixing ozone and liquid hydrocarbon in a reactor can form an explosivemixture, the use of ozone is better suited for the second embodiment inwhich an aqueous mixture is pretreated by mixing with ozone andsubjecting the mixture to ultrasonic cavitation.

The inventive methods optionally utilize a catalyst to catalyze theoxidation process. The catalyst may be one or more of iron, nickel,vanadium, or molybdenum, typically as a solid particulate or supportedcatalyst.

The disclosed methods utilize an acid to promote the oxidation reaction.The acid may be an organic acid or an inorganic acid. Examples oforganic acids include non-oxidizing acids such as acetic acid, formicacid, oxalic acid, propionic acid, or benzoic acid. Examples ofinorganic acids include one or more mineral acids, such as sulfuricacid, nitric acid, hydrochloric acid, phosphoric acid, boric acid,hydrofluoric acid, hydrobromic acid, or perchloric acid.

The disclosed methods further include separating the liquid hydrocarbonproduct from light hydrocarbon gases, water, catalyst, and oxidationsource. According to one embodiment, separation is carried out by meansof phase separation. Unspent oxidation source, catalyst and acid can berecycled back into the reactor for further use in oxidatively treatingthe hydrocarbon and increasing cetane number. It is important to notethat one skilled in the art would use reaction conditions that minimizeformation of a tight emulsion. It is also desirable to prevent excessiveoxidation of the diesel, which can result in formation of polymer orprecipitates. It is also desirable to minimize oxidation ofsulfur-bearing molecules and formation of water-soluble sulfones, asdoing so can undesirably reduce product yields.

The diesel product separated from light hydrocarbon gases, water,catalyst and oxidation source can be further purified by extractionusing a polar solvent, such as a lower alcohol (e.g., methanol), toremove over-oxidized materials. Over-oxidized hydrocarbons are morepolar and less stable than the desirable diesel product. If left in thediesel, over-oxidized hydrocarbons can continue to react and formundesirable precipitates. The methanol and diesel separate into twophases—(1) a phase of higher polarity containing the methanol and morehighly oxidized hydrocarbons and (2) a more hydrophobic phase thatincludes less oxidized diesel and/or other hydrocarbons. Residual watercan also be removed in the more hydrophilic methanol phase or it can beremoved using a dehydrator.

By using the inventive process, the cetane number of a startingfeedstock material can be increased by at least about 15%, and sometimessubstantially more (e.g., by at least about 20%, 25%, 30%, 40%, 50%,60%, 75%, or 100%). Such processes also result in an increase in cetanenumber of at least 7.5, and sometimes substantially more (e.g., anincrease of at least about 10, 15, 20, 25, 30, 35, 40, 50, 60, or 75).The cetane number of liquid hydrocarbon product can be at least 55, andsometimes substantially more (e.g., at least about 60, 65, 70, or 75).

In some cases, the resulting product has a cetane number so high that itis best suited as a blending stock to raise the cetane number of a lowercetane diesel fuel rather than as a diesel fuel by itself. According toone embodiment, the blending stock can have a cetane number greater than60, and sometimes substantially more (e.g., at least about 65, 70, 75,80, 90, 100, 110, 125, or 140).

These and other advantages and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only illustrated embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 schematically illustrates an exemplary system for oxidativelyincreasing the cetane number of a liquid hydrocarbon;

FIG. 2 schematically illustrates an exemplary reactor that utilizesultrasound to create cavitation and intimately mix a liquid hydrocarbonand oxidation source;

FIG. 3 is a flow diagram of an exemplary method of oxidativelyincreasing the cetane number of a liquid hydrocarbon;

FIG. 4 schematically illustrates an alternative exemplary system foroxidatively increasing the cetane number of a liquid hydrocarbon;

FIG. 5 is a flow diagram of an alternatively exemplary method ofoxidatively increasing the cetane number of a liquid hydrocarbon; and

FIG. 6 schematically illustrates an alternative exemplary system foroxidatively increasing the cetane number of a liquid hydrocarbon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of exemplary methods and systems for increasingcetane number of a hydrocarbon feedstock will now be provided withspecific reference to figures illustrating preferred embodiments of theinvention.

Reference is now made to FIG. 1, which schematically illustrates anexemplary system 100 for increasing cetane number of a hydrocarbon.According to this embodiment, a hydrocarbon (HC) feedstock 102 is fedinto a cavitation reactor 106 together with additional reactants 104,which typically include an oxidation source, a catalyst, and an organicor inorganic acid in addition to the oxidation source. Although FIG. 1depicts a single cavitation reactor 106, it will be appreciated that aseries of rectors can be utilized, including multiple cavitationreactors or a cavitation reactor and one or more reactors that include aconventional stifling mechanism.

According to one embodiment, the hydrocarbon feedstock will have aboiling point, or boiling range, in a range of about 150° C. to about380° C. Although not a necessary feature of the liquid hydrocarbonfeedstock, but due to the nature of the materials being treated, theliquid hydrocarbon feedstock may have sulfur content in a range of about10 to about 5000 ppm. The inventive methods and systems aim to minimizethe oxidation of sulfur-containing compounds in the feedstock. Excessiveoxidation can transform the sulfur-containing compounds into oxygenatedcompounds that are more water rather than oil soluble, thereby reducingthe yield of the upgraded product.

The hydrocarbon feedstock may be from a refinery stream (e.g., astraight run, thermally cracked hydrocarbons, catalytically crackedhydrocarbons, or hydrocracked hydrocarbons), biodiesels, vegetable oils,or animal fats. Examples of vegetable oils that can be used inconnection with the inventive methods and systems include palm oil,colza oil, pine oil, soya oil, sunflower oil, maize oil, safflower oil,cottonseed oil, coriander oil, mustard oil, or tall oil. An example ofanimal fat is tallow oil. The feedstock is typically not naphtha (i.e.,gasoline) and has a boiling range above that of naphtha.

Examples of biodiesels that may be used as part or all of the liquidhydrocarbon feedstock include biodiesels created via chemical reactionof methanol with vegetable oil according to the following reaction:

Methanol+oil===→biodiesel fuel

The result is a fatty acid methyl ester having the formulaC_(m)H_(n)O₂CH₃.

Alternatively, or in addition, the liquid hydrocarbon feedstock may begenerated from a visbreaker tailored to crack bright stock, usedlubricating oil, or gas oil with a boiling point in a range of about200° C. to about 500° C. The liquid hydrocarbon feedstock may include orbe derived from other materials, such as light catalytic cracking gasoil, light coker gas oil, light virgin gas oil, or kerosene. It will beappreciated that a wide variety of materials may be used for the liquidhydrocarbon feedstock so long as they yield a diesel fuel product havingan increased cetane number.

Examples of an “oxidation source” as used herein is a peroxide material,which is typically a compound of the molecular structure:

R₁—O—O—R₂

wherein, R₁ and R₂ are singly or collectively a hydrogen atom, anorganic group, or an inorganic group. Examples of peroxides in which R₁is an organic group and R₂ is a hydrogen include water-soluble peroxidessuch as methyl hydroperoxide (i.e., peroxy formic acid), ethylhydroperoxide (i.e., peroxy acetic acid), isopropyl hydroperoxide,n-butyl hydroperoxide, sec-butyl hydroperoxide, tert-butylhydroperoxide, 2-methoxy-2-propyl hydroperoxide, tert-amylhydroperoxide, and cyclohexyl hydroperoxide. Examples of peroxides inwhich R₁ is an inorganic group and R₂ is a hydrogen includeperoxonitrous acid, peroxophosphoric acid, and peroxosulfuric acid. Apreferred peroxide is hydrogen peroxide (i.e., in which both of R₁ andR₂ are hydrogen atoms). A wide variety of different peroxides or otheroxidation sources can be utilized so long as they assist in oxygenatingthe liquid hydrocarbon feedstock and result in a diesel fuel producthaving increased cetane number. Ozone can function as the oxidationsource but is best suited for pretreating an aqueous mixture comprisingwater and acid (FIGS. 4 and 5) rather than mixing directly with a liquidhydrocarbon feedstock, as that can form an explosive mixture.

According to one embodiment, the amount of peroxide or other oxidationsource used per kilogram of liquid hydrocarbon feedstock may be lessthan 300 g, though typically it is at least about 10 g and may rangefrom about 25 g to 300 g hydrogen peroxide per kilogram of liquidhydrocarbon feedstock. The hydrogen peroxide may be employed in the formof an aqueous solution containing, for example, and most typically, fromapproximately 10% to 70% by weight of hydrogen peroxide. If a differentperoxide is used in the absence of hydrogen peroxide, it is typicallyemployed in the same molar quantities as hydrogen peroxide. If adifferent peroxide is used in combination with hydrogen peroxide, thecumulative molar ratio of such other peroxide and hydrogen peroxide canbe the same as that of hydrogen peroxide used by itself. If ozone isused in combination with hydrogen peroxide, the concentration ofhydrogen peroxide may be less than 50%. Generally, it is not recommendedto use ozone alone as the oxidation source because the combination ofhydrocarbon and ozone can create an explosive environment in theprocess. If ozone is utilized in the cavitation reactor 106, the reactoris advantageously equipped with a conduit or other means for ventingexcess ozone through the top of the cavitation reactor 106 (See FIG. 4,elements 408, 413).

The acid may be a non-oxidizing organic acid, for example an acidselected from among formic acid, acetic acid, oxalic acid, propionicacid, or benzoic acid. Formic acid is a preferred organic acid.Alternatively, or in addition, the acid may be an inorganic acid, forexample a mineral acid selected from sulfuric acid, nitric acid,hydrochloric acid, phosphoric acid, boric acid, hydrofluoric acid,hydrobromic acid, or perchloric acid. Sulfuric acid is a preferredinorganic acid. The molar ratio of acid/hydrogen peroxide preferablyranges from about 0.01 to about 1, and even more preferably from about0.1 to about 0.5.

The catalyst may be any catalyst that can promote the oxidation of theliquid hydrocarbon feedstock in the presence of the oxidation source andacid. Examples of suitable catalyst metals include, but are not limitedto, iron, nickel, vanadium and molybdenum. The catalysts may be in theform of solid particulates, either alone or on an appropriate supportmaterial (e.g., silica or alumina). Alternatively, the catalysts may bein the form of fine particulates, such as ferric oxide.

The hydrocarbon feedstock 102 will comprise the oil phase entering thecavitation reactor 106, and the oxidation source, catalyst and organicor inorganic acid will comprise the aqueous phase entering thecavitation reactor 106. The catalyst may also form a separate solidphase before or during the reaction.

The cavitation reactor 106 can be any reactor that is able to createcavitation with intimate, high energy mixing of the oil phase andoxidation source in the aqueous phase within the reactor. The reactorwill also preferably generate cavitation in the liquidhydrocarbon/oxidation source. According to one embodiment, thecavitation reactor 106 is an ultrasonic cavitation reactor thatgenerates acoustic cavitation. According to another embodiment, thecavitation reactor 106 includes a spinning rotor capable of creatingmechanical cavitation. According to yet another embodiment, thecavitation reactor 106 is configured to generate cavitation by means ofan oscillating magnetic field. Cavitation can alternatively be createdby hydrodynamic flow of the liquid reactants. In other embodiments, thecavitation reactor 106 can employ optic cavitation (e.g., by laserpulses) or particle cavitation (e.g., by proton or neutrino pulses).

The operating temperature of the cavitation reactor can be in a range ofabout 20° C. to about 200° C., or a range of about 30° C. to about 180°C., or range of about 40° C. to about 80° C. In order to control thetemperature inside the cavitation reactor, it may be desirable toutilize cooling means known in the art, such as, by way of example, oneor more cooling or heat exchange coils (e.g., utilizing liquid water)positioned within the reactor. In some embodiments, the temperatureinside the cavitation reactor is in a range of 20° C. to 120° C., andpreferably less than 100° C. (e.g., less than 90° C., 80° C., 70° C.,65° C., or 60).

To prevent overheating and excessive formation of water-solublesulfones, the hydrocarbon feedstock is preferably at a temperature at orbelow 75° C. when introduced into cavitation reactor. By way of example,the temperature of the hydrocarbon feedstock can be 70° C. or less whenintroduced into cavitation reactor (e.g., no higher than 68° C., 65° C.,60° C., 55° C., 50° C., 45° C., 40° C., 35° C., or 30° C.).

The operating pressure of the cavitation reactor can be in a range ofabout 1 bar to about 30 bars, preferably in a range of about 3 bars toabout 25 bars, and more preferably in a range of about 5 bars to about20 bars.

Referring to FIG. 1, the reactants are maintained within the cavitationreactor 106 for a time sufficient to carry out the desired oxygenationreaction in order to raise the cetane number of the liquid hydrocarbonproduct relative to the hydrocarbon feedstock. The reaction time istypically in a range of about 30 seconds to about 90 minutes, or in arange of about 1 minute to about 45 minutes, or in a range of about 2minutes to about 30 minutes.

In general, it will be desirable to control the temperature, pressureand reaction time in order to promote beneficial oxygenation reactionswhile substantially preventing detrimental oxygenation reactions. Forexample, beneficial oxygenation reactions include oxygenating week H—Cbonds of aromatic and hydroaromatic compounds, particularly at thebenzylic position. Such oxygenation reactions increase the cetane numberof the diesel. Examples of detrimental oxygenation reactions thatdecrease the cetane number of the diesel include oxidation of strongprimary, secondary and tertiary alkyl H—C bonds found in paraffins andcycloparaffins, or oxidation of aromatics at non-benzylic positions,such as in the ring, to form phenol. In order to promote thermal andstorage stability, it may be advantageous to keep the oxygenate levelbetween about 0.5% to about 1%.

One exemplary embodiment of an ultrasonic reactor is more particularlyshown in FIG. 2. Reactor 200 shown in FIG. 2 includes a reactor vessel202 containing reactants 204. The reactants include an oil phase and anaqueous phase, and possibly also a gaseous phase, as described herein. Afirst ultrasonic emitter 206 a is positioned at the top end of reactorvessel 202, and a second ultrasonic emitter 206 b is positioned at thebottom end of reactor vessel 202. The ultrasonic emitters 206 produceultrasonic waves 208, which propagate throughout the entire volume ofreactor vessel 202. The ultrasonic waves 208 and waves created bycavitation cause intimate, high energy mixing of the oil and aqueousreactants 204 within the reactor vessel 202.

In general, ultrasonic energy in accordance with the reaction vessel 106of inventive system 100 is applied by the use of ultrasonics, which aresound-like waves whose frequency is above the range of normal humanhearing, i.e., above 20 kHz (20,000 cycles per second). Ultrasonicenergy with frequencies as high as 10 gigahertz (10,000,000,000 cyclesper second) has been generated, but for purposes of this invention,useful results will be achieved with frequencies in a range of about 20kHz to about 200 kHz, and preferably in a range of about 20 kHz to about50 kHz. Ultrasonic waves can be generated from mechanical, electrical,electromagnetic, or thermal energy sources. The intensity of the sonicenergy may also vary widely. For the purposes of this invention, desiredresults will generally be achieved with an intensity ranging from about30 watts/cm² to about 300 watts/cm², or preferably from about 50watts/cm² to about 100 watts/cm². One exemplary electromagnetic sourcecan be a magnetostrictive transducer, which converts magnetic energyinto ultrasonic energy by applying a strong alternating magnetic fieldto certain metals, alloys or ferrites. The typical electrical source isa piezoelectric transducer, which uses natural or synthetic singlecrystals (such as quartz) or ceramics (such a barium titanate or leadzirconate) and applies an alternating electrical voltage across oppositefaces of the crystal or ceramic to cause an alternating expansion andcontraction of crystal or ceramic at the impressed frequency. Thevarious methods of producing and applying ultrasonic energy, andcommercial suppliers of ultrasound equipment, are well known among thoseskilled in the use of ultrasound.

One exemplary ultrasonic reactor is available from Hielscher UltrasonicsGmbH, which is located in Teltow, Germany. According to the productliterature relating to this product, the exposure of liquids toultrasonic waves of high intensity causes acoustic cavitation. “Acousticcavitation” (and other forms of “cavitation”) is the formation andsubsequent violent collapse of small vacuum (cavitation) bubbles.Locally, extreme conditions arise from the violent collapse of eachbubble. Localized temperatures can be as high as 5000 Kelvin. Localizedpressures can be up to 2000 atmospheres. Liquid jets can form at up to1000 km/hr. Such conditions promote a better surface chemistry ofcatalysts by enhancing micro-mixing. In particular, the high localtemperature changes the chemical reaction kinetics of the oxidationprocess.

After the liquid hydrocarbon has been converted into a liquidhydrocarbon product of higher cetane number (e.g., diesel fueladditive), the reactants are transferred from the cavitation reactor 106into a phase separator 108. The phase separator causes or permitsdifferent fractions to separate into phases, thereby effecting theirseparation. Light hydrocarbon gases 110 are removed from the top becausethey are volatile and in gaseous form rather than liquid.

The main liquid hydrocarbon product 112 is removed by phase separationfrom the main aqueous phase. The liquid hydrocarbon product 112 willcontain both liquid hydrocarbon product and residual water, which isremoved using a dehydrator known to those of skill in the art.Dehydration can be effected using heat and/or chemical extraction.

The main aqueous phase can be further divided using known means into afirst fraction 114 comprised of water, spent catalyst, and spentoxidation source and a second fraction 116 comprised of recycleoxidation source, recycle catalyst, and recycle organic or inorganicacid. The second fraction 116 comprised of recycle materials can bereturned to the ultrasonic reactor 106.

The dehydrated liquid hydrocarbon product can be further purified byextracting over-oxidated hydrocarbons with a polar solvent, such as alower alcohol (e.g., methanol, ethanol or isopropyl alcohol) to form awashed hydrocarbon product. The more polar constituents, such asover-oxidized hydrocarbons and residual water, collect in the methanolphase, which separates from the more hydrophobic oil phase containingless oxidized hydrocarbons. It may be desirable to remove over-oxidizedhydrocarbons because they are more polar and less stable than thedesired liquid hydrocarbon product. If left in the hydrocarbon product,the over-oxidized hydrocarbons can continue to react, resulting inundesirable precipitates. In some cases, extraction with a polar solventcan also remove residual water from the liquid hydrocarbon product.

FIG. 3 is a flow chart that illustrates an exemplary method 300 ofincreasing the cetane number of a liquid hydrocarbon (e.g., using thesystem 100 shown in FIG. 1 and/or the ultrasonic reactor 200 shown inFIG. 2). A first step 302 includes providing a liquid hydrocarbon,oxidation source, catalyst and acid as described herein. The second step304 involves mixing the liquid hydrocarbon, oxidation source, catalystand acid using ultrasonic waves, or ultrasonic cavitation to effect highenergy mixing. This results in the third step 306, which includesreacting the mixture at a desired temperature, pressure and time toyield a liquid hydrocarbon product having increased cetane number. Thefourth step 308 includes separating the liquid hydrocarbon from gaseoushydrocarbons and also water, catalyst, oxidation source, and acid. Thefifth step 310 includes extracting over-oxidized hydrocarbons from theliquid hydrocarbon to form a washed hydrocarbon product in the oil phaseand over-oxidized hydrocarbons in the polar solvent phase. Removing theover-oxidized hydrocarbons yields a more stable end product.

FIG. 4 schematically depicts an alternative embodiment of a reactionsystem 400 for increasing the cetane number of a liquid hydrocarbon. Inthis embodiment, an aqueous mixture 402 comprised of water and anorganic or inorganic acid is pretreated by mixing and reacting theaqueous mixture 402 with ozone 404 within a pretreating cavitationreactor 406. The pretreating cavitation reactor 406 can be any reactorthat is able to cause the ozone to form reactive hydroxyl radicalsand/or oxygen radicals within the pretreated aqueous mixture. Excessozone 408 can be removed from the top of cavitation reactor 406 througha conduit or other venting means known in the art. One example of acavitation reactor is an ultrasound reactor, which may be the same orsimilar to the ultrasound reactor described above and used in reactingthe liquid hydrocarbon feedstock with the oxidation source. Othercavitation reactors can create cavitation by a spinning rotor,oscillating magnetic field, hydrodynamic flow, optic cavitation, orparticle cavitation.

The pretreatment time of the aqueous mixture with ozone in thepretreatment reactor 406 can be in a range of about 30 seconds to about10 minutes, preferably in a range of about 45 seconds to about 8minutes, and more preferably in a range of about 1 minute to about 5minutes. The temperature may be room temperature (i.e., about 20-25° C.)and the pressure may be 1 bar to about 30 bars, preferably about 3 barsto about 25 bars, and more preferably about 5 bars to about 20 bars.

The pretreated aqueous mixture from pretreatment reactor 406 and liquidhydrocarbon feedstock 412 are introduced into upgrading reactor 410,which includes means for mixing the liquid hydrocarbon feedstock andpretreated aqueous mixture together. At least some of the excess ozone408 from pretreatment reactor 406 can also be introduced into upgradingreactor 410. According to one embodiment, mixing may be provided atleast in part by mechanical stirring. According to another embodiment,mixing may be provided at least in part by ultrasonic cavitation. Acombination of mechanical mixing and ultrasonic cavitation may beprovided within upgrading reactor 410 in order to promote beneficialoxygenation reactions between hydroxyl radicals provided by thepretreated aqueous mixture and the liquid hydrocarbon. As in theembodiment described above relative to FIG. 1, a series of upgradingreactors can be included, which utilize one or both of mechanicalstirring or ultrasonic cavitation. The reactants are maintained withinthe upgrading reactor 410 for a time and at a temperature and pressuresufficient to carry out the desired oxygenation reaction in order toraise the cetane number of the liquid hydrocarbon product relative tothe liquid hydrocarbon feedstock (e.g., see time, temperature andpressures set forth above relative to the embodiment of FIG. 1). Gases413 can be removed from the top of upgrading reactor 410.

After the liquid hydrocarbon has been converted into a liquidhydrocarbon product having a higher cetane number (e.g., diesel fueladditive), the reactants are transferred from the upgrading reactor 410into a liquid/liquid separator 414, which separates an upgradedhydrocarbon product 416 from water and acid. Recycle water and acid 418can be introduced back into cavitation reactor 406. Excess (or “spent”)water and acid 420 are separated from the recycle water and acid anddiscarded. The hydrocarbon product 416 can be further washed using apolar solvent (e.g., methanol) to yield a washed hydrocarbon product 422that is separated by phase separation from over-oxidized hydrocarbons424 in a polar solvent phase.

FIG. 5 is a flow chart that illustrates an exemplary method 500 ofincreasing the cetane number of a liquid hydrocarbon (e.g., using thesystem 400 shown in FIG. 4 and/or the ultrasonic reactor 200 shown inFIG. 2). In a first step 502 water, acid and ozone are provided. Thewater and acid are typically provided as an aqueous mixture and theozone as a separate stream. In a second step 504, the aqueous mixtureand ozone are subjected to ultrasonic cavitation in order to form apretreated aqueous mixture having reactive hydroxyl radicals formedtherein. In a third step 506, the pretreated aqueous mixture is mixedand reacted together with a liquid hydrocarbon feedstream in order toyield an upgraded liquid hydrocarbon having an increased cetane number.In a fourth step 508, the upgraded liquid hydrocarbon product isseparated from the water and acid. In a fifth step 510, over-oxidizedhydrocarbons are extracted from the desired product using a polarsolvent (e.g., methanol) to form a washed hydrocarbon product that ismore stable and less reactive.

FIG. 6 schematically depicts an alternative embodiment of a reactionsystem 600 for increasing the cetane number of a liquid hydrocarbon. Inthis embodiment, an aqueous mixture 602 comprised of water and anorganic or inorganic acid, ozone 604, and a portion of a liquidhydrocarbon feedstock 612 are reacted together in a first cavitationreactor 606. The first cavitation reactor 606 can be any reactor that isable to create cavitation, as discussed herein. Excess ozone 408 can beremoved from the top of first cavitation reactor 406 through a conduitor other venting means known in the art.

The reactants from first cavitation reactor 606, excess ozone 608, and asecond portion of the liquid hydrocarbon feedstock 412 are introducedinto second upgrading reactor 610, which includes means for mixing thereactants together. According to one embodiment, mixing may be providedat least in part by mechanical stirring. According to anotherembodiment, mixing may be provided at least in part by cavitation, asdiscussed herein. A combination of mechanical mixing and ultrasoniccavitation may be provided within second upgrading reactor 610 in orderto promote beneficial oxygenation reactions of the liquid hydrocarbon.The reactants are maintained within the first cavitation reactor 606 andsecond upgrading reactor 610 for a time and at a temperature andpressure sufficient to carry out the desired oxygenation reaction inorder to raise the cetane number of the liquid hydrocarbon productrelative to the liquid hydrocarbon feedstock (e.g., see time,temperature and pressures set forth above relative to the embodiment ofFIG. 1).

After the liquid hydrocarbon has been converted into a liquidhydrocarbon product having a higher cetane number (e.g., diesel fueladditive), the reactants are transferred from the second upgradingreactor 610 into a liquid/liquid separator 614, which separates anupgraded hydrocarbon product 616 from water and acid. Recycle water andacid 618 can be introduced back into first cavitation reactor 606.Excess (or “spent”) water and acid 620 are separated from the recyclewater and acid and discarded. The upgraded hydrocarbon product 616 canbe washed using a polar solvent (e.g., methanol) to extractover-oxidized hydrocarbons and yield a washed hydrocarbon product 622that is in a separate phase from the over-oxidized hydrocarbons 624.This waste polar fraction can be discarded as desired or it can be usedas a fuel where heat is desired to drive a reaction.

The product that is produced by the foregoing systems and methodsincludes oxygenated hydrocarbon species. Oxygenates blended into dieselfuel can serve at least two purposes. First, they can improve cetanenumber compared to non-oxygenated diesel fuel. Components based onrenewable feedstocks can provide the added benefit of reducing netemissions of greenhouse gases in the form of carbon dioxide emissions.Second, oxygenates blended into diesel fuel helps reduce particulateemissions and also oxides of nitrogen (NOx).

The foregoing systems and methods yield a product that typically has acetane number of 55 or higher, typically greater than about 60, 65, 70,or 75. In some cases, the product can be characterized as “super cetanediesel” that can be used as a blending stock for diesel fuels havingcetane numbers below a specific minimum standard (e.g., between 40 to75) in order to yield blended diesel fuels having a desired cetanenumber at or above the specific minimum standard. Super cetane materialscan have a cetane number that is substantially higher than 60 (e.g., atleast about 65, 70, 75, 80, 90, 100, 110, 125, or 140).

By using the disclosed process, the cetane number of a hydrocarbonfeedstock material can be increased by at least about 15%, at leastabout 20%, at least about 25%, at least about 30%, at least about 40%,at least about 50%, at least about 60%, at least about 75%, or at leastabout 100%. Such processes also result in an increase in cetane numberof at least 7.5, 10, 15, 20, 25, 30, 35, 40, 50, 60, or 75. The cetanenumber of liquid hydrocarbon product can be at least 55, 60, 65, 70, 75,80, 90, 100, 110, 125, or 140.

The following examples of the invention are given by way of illustrationonly, and not by limitation. They are provided in order to illustrateparticular methodologies for carrying out the invention. It will beunderstood that there are other ways, including other reactionconditions and reactants, that can be used to carry out the inventiondescribed herein.

For Examples 1-6, batch oxidation tests were conducted in a beaker usingthe following components:

Diesel—beginning cetane number=52

Acetic acid—100% purity; density=1.05 g/ml

Formic acid>98% purity; density=1.22 g/ml

Aqueous hydrogen peroxide—30% concentration; density=1.463 g/ml

Ozone—containing <1% ozone in a stream of air

Distilled water

Ultrasound device—Hielscher UP400S (400 watts, 24 kHz)

Comparative Example 1

With reference to U.S. Pat. No. 5,114,434, 300 ml of diesel and 30 ml ofaqueous hydrogen peroxide were placed into in a 500 ml beaker andvigorously stirred for 10 minutes at 25° C. using a magnetic stirrer.The resulting diesel product was then vigorously stirred with methanolin a ratio of 1 part methanol to 1 part diesel product to extractover-oxidized reaction products. The methanol washed diesel product wasinjected into an IQT machine manufactured by Advanced Engine Technology.The methanol washed diesel product as prepared according to theprocedure described in U.S. Pat. No. 5,114,434 had a measured cetanenumber of 57, which was an increase of 5 over the initial cetane numberof the starting diesel material.

Example 2

An aqueous solution comprised of 50 ml of acetic acid and 150 ml ofdistilled water was placed into a 500 ml beaker. A Hielscher UP400Sultrasound device was inserted into the beaker. Thereafter a stream ofozone-containing air was bubbled into the aqueous solution while theultrasound device was turned on at 100% amplitude for 5 minutes. Theresulting ozone-treated aqueous solution and 200 ml of diesel werevigorously stirred for 10 minutes using a magnetic stirrer. Theresulting diesel product was then vigorously stirred with methanol (in aratio of 1 part methanol to 1 part diesel) to extract over-oxidizedreaction products. The diesel introduced into the reactor was notpre-heated and was about 30° C. or below, and the temperature of thereactor was controlled using cooling or heat exchange and was kept below50° C. The temperature of the reaction was controlled using cooling orheat exchange and was kept below 50° C. The methanol washed dieselproduct was injected into an IQT machine and determined to have ameasured cetane number of 60.4, which was an increase of 8.4 over theinitial cetane number of the starting diesel material.

Example 3

An aqueous solution consisting of 5 ml formic acid, 25 ml aqueoushydrogen peroxide, and 70 ml distilled water was placed into a 500 mlbeaker together with 300 ml of diesel. A Hielscher UP400S ultrasounddevice was inserted into the beaker. Thereafter a stream ofozone-containing air was bubbled through the aqueous and diesel phaseswhile the ultrasound device was turned on at 100% amplitude for 5minutes. The diesel introduced into the reactor was not pre-heated andwas about 30° C. or below, and the temperature of the reactor wascontrolled using cooling or heat exchange and was kept below 50° C. Avery thick emulsion was formed at the end of test. The emulsion brokewithin 60 minutes. The resulting diesel product was washed with methanolas in Example 2 to extract over-oxidized reaction products. The methanolwashed diesel product was injected into an IQT machine and determined tohave a measured cetane number of 61, which was an increase of 9 over theinitial cetane number of the starting diesel material.

Example 4

An aqueous solution consisting of 5 ml formic acid, 25 ml aqueoushydrogen peroxide was placed into a 500 ml beaker together with 300 mlof diesel. A Hielscher UP400S ultrasound device was inserted into thebeaker. Thereafter a stream of ozone-containing air was bubbled throughthe aqueous and diesel phases while the ultrasound device was pulsed ata mode of 0.3 and 40% amplitude for 10 minutes. The diesel introducedinto the reactor was not pre-heated and was about 30° C. or below, andthe temperature of the reactor was controlled using cooling or heatexchange and was kept below 50° C. An emulsion was observed to forminstantaneously, but which also broke rapidly. The resulting dieselproduct was washed with methanol to extract over-oxidized reactionproducts. The methanol washed diesel product was injected into an IQTmachine and determined to have a measured cetane number of 62.0, whichwas an increase of 10 over the initial cetane number of the startingdiesel material.

Example 5

An aqueous solution consisting of 5 ml formic acid, 25 ml aqueoushydrogen peroxide, and 70 ml distilled water was placed into a 500 mlbeaker together with 300 ml of diesel. A Hielscher UP400S ultrasounddevice was inserted into the beaker and the mixture was subjected toultrasound at 100% amplitude for 10 minutes. The diesel introduced intothe reactor was not pre-heated and was about 30° C. or below, and thetemperature of the reactor was controlled using cooling or heat exchangeand was kept below 50° C. A very thick emulsion was formed at the end oftest. The emulsion broke within 60 minutes. The resulting diesel productwas washed with methanol as in previous examples to separate it fromover-oxidized reaction products. The methanol washed diesel product wasinjected into an IQT machine and determined to have a measured cetanenumber of 64.2, which was an increase of 12.2 over the initial cetanenumber of the starting diesel material.

Example 6

An aqueous solution consisting of 5 ml formic acid and 5 ml of aqueoushydrogen peroxide was placed into a 500 ml beaker together with 300 mlof diesel. A Hielscher UP400S ultrasound device was inserted into thebeaker and the mixture was subjected to ultrasound at 100% amplitude for10 minutes while ozone containing air was continuously bubbled into theaqueous solution. The diesel introduced into the reactor was notpre-heated and was about 30° C. or below, and the temperature of thereactor was controlled using cooling or heat exchange and was kept below50° C. An emulsion formed, which broke within 30 minutes after the test.The resulting diesel product was washed with methanol as in previousexamples. The methanol washed diesel product was injected into an IQTmachine and determined to have a cetane number of 62.4, which was anincrease of 10.4 over the initial cetane number of the starting dieselmaterial.

For comparison purposes, the conditions and results of Examples 1-6 areset forth in Table 1 below:

TABLE 1 Example 1A 2 3 4 5 6 Acid-acetic(A) or 50 ml-(A) 5 ml-(F) 5ml-(F) 5 ml-(F) 5 ml-(F) formic(F) Hydrogen peroxide, ml 30 ml 25 25 255 Distilled water, ml 150 70 70 Ozone Yes Yes Yes None Yes Ultrasoundintensity Maximum Maximum 40% at Maximum Maximum 0.3 Time, minute 10 5 510 10 10 Magnetic stirrer yes Yes Diesel, ml 300 300 300 300 300 300Measured cetane 57.8 60.4 61 62 64.2 62.4 number Change in cetane 5.88.4 9 10 12.2 10.4 number compared to original diesel Percentage changein 11.2% 16.2% 17.3% 19.2% 23.5% 20% cetane number compared to originaldiesel

As seen in Table 1, all test conditions that were run according to thepresent invention (Examples 2-6) show a significantly higher increase incetane number compared to the test that was run according to ComparativeExample 1. Introducing ultrasound into the reaction vessel, even forjust 5 minutes, significantly increased the cetane number overComparative Example 1, which is a surprising and unexpected result. Incontinuous flow tests and at optimum conditions, the inventors expectmuch higher cetane numbers using the inventive process.

In addition, the conditions employed in Examples 2-6 selectivelypromoted oxidation of hydrocarbons in the diesel material whileminimizing oxidation of sulfur-bearing molecules and formation ofwater-soluble sulfones. In this way, the yield of product in thenon-aqueous phase was significantly higher than in Comparative Example7, below, in which most of the sulfur-bearing components were oxidizedto form water-soluble sulfones and were removed in the aqueous phase.

Comparative Example 7

With reference to U.S. Pat. No. 6,500,219, an illustrativedesulfurization system used a stainless steel ultrasound chamber havingan internal volume of 3 liters, and diesel fuel and water as the fossilfuel and aqueous fluids, respectively, at three parts by volume ofdiesel fuel to one part by volume of water. The diesel fuel waspreheated to a temperature of about 75° C.; the water was not preheated.The hydroperoxide was hydrogen peroxide, added to the water as a 3% (byweight) aqueous solution, at 0.0025 parts by volume of the solution toone part by volume of the water. The surface active agent was extraheavy mineral oil, obtained from Mallinckrodt Baker Inc., Philipsburg,N.J., USA, added to the diesel at approximately 0.001 part by volume ofthe mineral oil to one part by volume of the diesel. The entire mixturewas passed into the ultrasound at a flow rate of approximately 1 gallonper minute (3.8 liters/min) at approximately atmospheric pressure. Theultrasound chamber contained a metal (stainless steel) screen on whichrested approximately 25 grams each of silver and nickel pellets, eachapproximately one-eighth inch (0.3 cm) in diameter. There is no mentionof the reactor being cooled anytime during the reaction process.

According to U.S. Pat. No. 6,500,219 “The ultrasound-promoted oxidationthat occurs in the practice of this invention [was] selective toward thesulfur-bearing compounds of the fossil fuel, with little or no oxidativeeffect in the non-sulfur-bearing components of the fuel” (col. 3, lines5-9). The conditions employed in Comparative Example 7 thereforepromoted oxidation of the sulfur-bearing compounds with little or nooxidative effect in the non-sulfur-bearing components.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A method for increasing cetane number of ahydrocarbon, comprising: providing a hydrocarbon feedstock having aboiling range above that of naphtha; introducing the hydrocarbonfeedstock, an oxidation source, a water-soluble acid in addition to theoxidation source, and optionally a catalyst into a cavitation reactor;and operating the cavitation reactor with cooling or heat exchange tocontrol the temperature inside the cavitation reactor, promotecetane-increasing oxygenation reactions between the hydrocarbonfeedstock and oxidation source, minimize formation of water-solublesulfones, and yield liquid hydrocarbon product having a cetane number atleast 15% higher than the cetane number of the hydrocarbon feedstock. 2.A method as in claim 1, the hydrocarbon feedstock comprising at leastone material selected from the group consisting of refinery streams,straight petroleum runs, thermally cracked hydrocarbons, catalyticallycracked hydrocarbons, hydrocracked hydrocarbons, biodiesels, vegetableoils, animal fats, and a material produced by visbreaking at least oneof bright stock, used lubricating oil, or gas oil with a boiling pointin a range of about 200° C. to about 500° C.
 3. A method as in claim 1,the hydrocarbon feedstock having an initial temperature below 70° C.when introduced into the cavitation reactor, the cavitation reactoroperating at a temperature in a range of about 20° C. to about 120° C.,at a pressure in a range of about 1 bar to about 30 bars, and for a timeperiod in a range of about 30 seconds to about 90 minutes.
 4. A methodas in claim 1, the hydrocarbon feedstock having an initial temperaturebelow 68° C. when introduced into the cavitation reactor, the cavitationreactor operating at a temperature of 68° C. or less, at a pressure in arange of about 2 bars to about 25 bars, and for a time period in a rangeof about 1 minute to about 45 minutes.
 5. A method as in claim 1,further comprising operating one or more additional cavitation reactorsto promote cetane-increasing reactions involving the hydrocarbonfeedstock and/or the liquid hydrocarbon product.
 6. A method as in claim1, the oxidation source comprising at least one of aqueous hydrogenperoxide, organic peroxide, inorganic peroxide, or ozone.
 7. A method asin claim 1, the cavitation reactor operating using a catalyst comprisingat least one metal selected from iron, nickel, vanadium, or molybdenum.8. A method as in claim 1, the acid comprising at least onenon-oxidizing organic acid.
 9. A method as in claim 1, the acidcomprising at least one mineral acid.
 10. A method as in claim 12, themineral acid comprising at least one of sulfuric acid, nitric acid,hydrochloric acid, phosphoric acid, boric acid, hydrofluoric acid,hydrobromic acid, or perchloric acid.
 11. A method as in claim 1,wherein cavitation is provided by ultrasonic cavitation.
 12. A method asin claim 1, wherein cavitation is provided by one or more of a spinningrotor, an oscillating magnetic field, hydrodynamic flow of liquidreactants within the cavitation reactor, optic cavitation, or particlecavitation.
 13. A method as in claim 1, further comprising separatingthe liquid hydrocarbon product from at least one of light hydrocarbongases, water, catalyst, or oxidation source by phase separation.
 14. Amethod as in claim 1, further comprising: introducing an oxidizer and anaqueous mixture comprised of water and acid into an ultrasoniccavitation reactor; subjecting the aqueous mixture and oxidizer toultrasonic cavitation to yield a pretreated aqueous mixture; andintroducing the pretreated aqueous mixture into the cavitation reactor,the pretreated aqueous mixture providing at least a portion of theoxidation source and the water-soluble acid.
 15. A method as in claim14, wherein the oxidizer comprises ozone.
 16. A method as in claim 1,the method yielding a diesel blending stock, the method furthercomprising blending the diesel blending stock with diesel fuel having acetane number less than a specified minimum value to yield a blendeddiesel product having a cetane number equal to or greater than thespecified minimum value.
 17. A method as in claim 1, wherein thespecified minimum value is in a range of 40 to
 75. 18. A method forincreasing cetane number of a hydrocarbon, comprising: providing ahydrocarbon feedstock comprising diesel or other hydrocarbon with aboiling range above that of naphtha; introducing the hydrocarbonfeedstock, an oxidation source, water, an acid comprising at least oneof a non-oxidizing organic acid or a mineral acid, and optionally acatalyst into a cavitation reactor; and operating the cavitation reactorwith cooling or heat exchange to maintain the temperature inside thecavitation reactor to below 120° C., promote cetane-increasingoxygenation reactions between the hydrocarbon feedstock and oxidationsource, minimize formation of water-soluble sulfones, and yield liquidhydrocarbon product having a cetane number at least 20% higher than thecetane number of the hydrocarbon feedstock.
 19. A method as in claim 17,the acid comprising at least one of sulfuric acid, nitric acid,hydrochloric acid, phosphoric acid, boric acid, hydrofluoric acid,hydrobromic acid, perchloric acid, formic acid, acetic acid, oxalicacid, propionic acid, or benzoic acid.
 20. A method for increasingcetane number of a hydrocarbon, comprising: providing a hydrocarbonfeedstock selected from the group consisting of comprising diesel, fueloils, kerosene, refinery streams having a boiling range above that ofnaphtha, biodiesels, vegetable oils, and animal fats or otherhydrocarbon with a boiling point or range above that of naphtha;introducing the hydrocarbon feedstock at a temperature below 68° C., anoxidation source, water, a water-soluble acid in addition to theoxidation source, and optionally a catalyst into a cavitation reactor;and operating the cavitation reactor while maintaining the temperatureinside the cavitation reactor below 70° C., promote cetane-increasingoxygenation reactions between the hydrocarbon feedstock and oxidationsource, minimize formation of water-soluble sulfones, and yield liquidhydrocarbon product having a cetane number at least 50% higher than thecetane number of the liquid hydrocarbon feedstock.